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Old 06-05-2016, 11:17   #1
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Battery system for 12V Windlass + 24V Bow Thruster

Been thinking of adding a bow thruster. For the size I need, the 24V models are appropriate. I already have a 12V windlass with a 12V starting battery in the bow. Charging this via a battery combiner from alternator, shore power or generator.

There are 24V convertors available that can charge two series connected 12V batteries for a bow thruster. The convertor charge output is only 10A, so its almost a trickle charge rate. Ideally one might add two more 12V batteries in the bow, dedicated to this 24V system and completely separated, electrically, from the windlass battery except for the 12V line back to the boat's charger.

I'm sure it's possible to use the existing windlass battery in series with another identical battery to form the 24V for the thruster, while leaving the connection to the first 12V battery in place for the windlass. But how to charge both batteries?

I have some ideas about this but I wondered if anyone else has solved this problem without needing a total of 3 batteries forward?

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Old 06-05-2016, 22:17   #2
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Re: Battery system for 12V Windlass + 24V Bow Thruster

don't center tap a bank (take 12v from the middle of a 24v). you'd need another 24v bank and leave the 12v alone. this seems like a silly way to go. I would look at 12v ones.

if you already have a charge line going to the 12v then you could use the 12v to 24v charger in the bow. but having 3 big enough batteries in the bow to run both just seems silly.

or consider changing the windlass to 24v. have a 24v bank in the bow charged by the existing pos line. with 12-24v charger back with other batteries. feeding 24v up the existing charge line.

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Old 07-05-2016, 09:49   #3
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Re: Battery system for 12V Windlass + 24V Bow Thruster

Thanks for your advice. I agree having 3 batteries in the bow is, or seems silly at first thought. But I think I've decided to go that way if I need the 24V.

Why 24V may be needed: I decided on an external thruster (higher efficiency and easier installation) and had to have at least 200lbs thrust (its a heavy boat with lots of windage). YachtThruster has one that requires 24V. SidePower has one that operates at 12V. I've not yet decided which one is better quality, but my research so far has me favoring YachtThruster.

At least the two additional 12V batteries can be rather smaller than the windlass battery. The current required could be as much as 200A@24V but would only be used for a maximum of 2 minutes while departing and docking. And lets say you needed to do that four times in one day with no charging in between. Means you need to draw out 200*8/60=27AH. They recommend 55AH batteries in series, so you'll have 50% discharge in this worst case scenario.
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Old 08-05-2016, 09:18   #4
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Re: Battery system for 12V Windlass + 24V Bow Thruster

200amps is surely a peak. Is there any one out there that has monitored usage while using it?

Also, since you need to run cable for a 24volt converter, consider running thick cable to serve windlas from batery bank and save one battery.

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Old 08-05-2016, 12:36   #5
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Re: Battery system for 12V Windlass + 24V Bow Thruster

24V for bow thruster from 12V idea here you might find interesting.
24 Volts from 12
An (expensive but effective and almost foolproof) option not yet mentioned would be to replace your windlass motor with a 24V one. Maybe could even find a free exchange if more people want a 12V motor.
Adding a 24V alternator to your engine boosts thruster/windlass battery bank at high current during use so less chance of running out of power. Or no new 24V alternator, just restrict 24V charging to mains charger from generator or shore power.
Only two batteries needed to serve both units this way assuming they're never used at the same time..
Maybe cheaper (but less effective and definitely not foolproof) is to switch two batteries between series and parallel as required. Charging can be at 12V (parallelled) by your existing alternator.
Obviously running the windlass at 24V needs to be prevented as does use of thruster while charging discharged batteries at 12V.
Just thinking aloud really, probably no help at all
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Old 08-05-2016, 12:58   #6
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Re: Battery system for 12V Windlass + 24V Bow Thruster

I have a Catalina 470 with a factory installed 7 hp SidePower 12v Bow Thruster. The bow thruster draws it power from the house bank, about 15 feet away.

The thruster works well and frankly I would not own another sailboat over 40 feet without one.

But if I had to do it over, I would have had the factory install a larger horsepower thruster. The current one doesn't work well in high winds (Over 15 kts.), which of course is when you need it most.

It sounds like you are going for the bigger size which is good.

Have you considered using a Hydraulic version instead?

Tom Jeremiason
Punta Gorda, Florida

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